1. Field of the Invention
The present invention relates to wireless power transmission in oil wells to downhole well equipment, using guided acoustic Lamb waves and with tubular conduits in the well serving as a power transmission medium.
2. Description of the Related Art
Reservoir management has been based on acquiring reservoir data captured by permanently installed sensors inside a well. These sensors were directly in contact with the reservoir to be monitored and provided real-time data concerning reservoir conditions for long-term and continuous reservoir management. One such reservoir management system is a permanent downhole monitoring system, or PDHMS, utilized by the assignee of the present application in what were referred to as smart wells.
Downhole permanent installations included both sensors and control valves. The sensors were used to monitor various physical and dynamical properties of the well, including temperature, pressure, and multiphase flow rates. In the case of smart wells, the sensors were combined with flow control devices to adjust fluid flow rate and optimize well performance and reservoir behavior. Electrical power was required to be provided to both sensors and flow control devices.
Other permanently deployed or installed downhole wellbore instrumentation applications where operating electrical power was required included sensors (geophones) for monitoring seismic or acoustic earth properties, formation pressure sensors, optical sensors, and electromagnetic field or EM sensors.
Usually these permanently deployed systems relied on cables run from surface to provide power to these devices. With these devices installed at depths of several thousands of feet inside a well, the use of cable was very expensive, as well as being and time-consuming to install. The use of cable was thus undesirable. Cable was also difficult to use in a wellbore along the tubing string whether integral to the well tubing or spaced in the annulus between well tubing and casing. Other disadvantages of using cables included reliability issues, complicated installation, and the risk of cable breaking because of the corrosion from well fluids, as well as heavy wear due to movement of the tubing string within the wellbore. A number of techniques have been proposed to eliminate cables and the associated problems to provide wireless transmission of power inside a well from the surface using a tubular conduit (production tubing or casing) as transmission medium.
Electromagnetic based power transmission methods allowed for an electrical signal to be injected into electrically conductive casings or tubing to create an electrical dipole source at the bottom of the well. U.S. Pat. No. 4,839,644 involved a tubing-casing electrical conduction transmission system in which an insulated system of tubing and casing served as a coaxial line to transmit both power and data. The system used an inductive coupling technique and a toroid was used for current injection. This required a substantially nonconductive fluid such as crude oil in the annulus between casing and tubing.
In U.S. Published Patent Application No. 2003/0058127 an electrically insulated conductive casing was used to establish electrical connection between surface and permanent downhole installations. Current was caused to flow to power downhole installations. U.S. Pat. No. 6,515,592 also used an electrically conductive conduit in the well with electrical insulation of a section of the conduit and insulation of the encapsulated section of conduit from an adjoining section by a conduit gap. The downhole device was coupled to insulated section and both power and data is transmitted. U.S. Pat. No. 7,114,561 used metal well casing for a power and data communication path between surface and downhole modules, with formation ground used as the return path to complete the electrical circuit.
U.S. Pat. No. 8,009,059 involved a downhole sensor energized with a surface pressure wave generator and a downhole mechanical to electrical energy converter. The energy converter took the form of magnetostrictive material or a piezoelectric crystal. U.S. Pat. No. 8,358,220 described a wellbore communication system using casing or tubing as transmission medium and employing electromagnetic coupling based technique.
Fiber optical cable and a solar cell were arranged inside a well in European Patent No. 1918508. Solar light was transmitted through the fiber optical cable in the wellbore such that the transmitted light illuminated a solar cell and the solar cell generated electricity for use by downhole well equipment. European Patent No. 1448867 discloses downhole power generators, which convert hydraulic energy into electrical energy.
Other methods for power transmission inside a well are described in European Patent No. 0721053; U.S. Pat. No. 6,415,869; European Patent No. 1252416; PCT Published Application WO 2002063341; European Patent No. 2153008; U.S. Pat. No. 7,488,194; U.S. Pat. No. 8,353,336; U.S. Pat. No. 5,744,877; and PCT Published Application WO 2011087400.
The methods which employed a toroid for current injection in casing, tubing, or a drill string were limited in the amount of power which could be inductively coupled. Also, the current loop would be local, as the current sought the shortest path that is through the casing. Another disadvantage of prior systems was that the wellhead necessarily had to be maintained at a very high electrical potential in order to achieve the desired current density at well bottom. Thus, so far as is known, the prior art had limitations including high operational and design complexity, limited power transfer, low or short transmission distance and low transmission efficiency.